1. Field of the Invention
The present invention relates to a sheet feeder, an image forming apparatus, and a sheet feeder control method.
2. Description of the Related Art
Generally, an image forming apparatus such as a copying machine is equipped with roller pairs which are called as aligning rollers. These aligning rollers are provided at a position of the upstream side in the conveying direction of an image forming apparatus (an unit to transfer a toner image on sheets conveyed using a photosensitive drum, etc.) and functions to correct the oblique ends of sheets conveyed from the sheet feeder.
The aligning rollers are rotated to properly correct sheets conveyed obliquely by bending sheets fed from the sheet feeder at the nip position by putting them to the nip position of the aligning rollers which are kept stopped to rotate and to send out the sheets at an optimum timing to transfer a toner image on the sheets at the image forming unit as described above.
The sheet feeder is provided at the upper-stream side in the conveying direction of the aligning rollers; however, feed rollers may be provided at the upper-stream side of the aligning rollers in the relation of the length of the conveying path from the sheet feeder to the aligning rollers. These feed rollers are to convey sheets supplied from the sheet feeder to the aligning rollers; but the aligning rollers are first in the rotation stopped state as described above, and for the reason that a prescribed flexion is formed on sheets, the feed rollers are stopped to rotate at a timing when the flexion formed on sheets by the aligning rollers reaches a specified amount.
This feed roller have no exclusive driving source and use the driving source jointly with other rollers (for example, sheet feed rollers, aligning rollers, etc.) in many cases. Because of this, as disclosed in the Japanese Patent Application Publication No. 2003-155138, the driving power of this feed roller is transmitted from the commonly using driving source via gears, etc. and further, the feed rollers are rotated or stopped using a clutch, etc. In other words, the rotation and stopping of the feed rollers are controlled by the ON/OFF of this clutch.
However, as the rotation/stopping of the feed roller is made by this clutch, when the driving power is transmitted/cut off from the driving source by the clutch, a sudden torque is applied to the driving shaft and vibration is generated. This vibration adversely affects especially the optical unit, the transfer belt, the photosensitive drum, etc. in the image forming apparatus, and gives a jitter to an image. In other words, this vibration is transmitted to a mirror of the optical system and laser light pitch is changed and an electrostatic latent image formed on the photosensitive drum may become uneven.